Biogeosciences Discuss., 7, 4045-4088, 2010
www.biogeosciences-discuss.net/7/4045/2010/
doi:10.5194/bgd-7-4045-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG.
Fueling primary productivity: nutrient return pathways from the deep ocean and their dependence on the Meridional Overturning Circulation
J. B. Palter1, J. L. Sarmiento1, A. Gnanadesikan2, J. Simeon3, and D. Slater1
1Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, New Jersey, USA
2Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA
3Laboratoire des Sciences du Climat et de l'Environnement, UMR CEA-CNRS, CEA Saclay, 91191 Gif-sur-Yvette, France

Abstract. In the Southern Ocean, mixing and upwelling in the presence of heat and freshwater surface fluxes transform subpycnocline water to lighter densities as part of the upward branch of the Meridional Overturning Circulation (MOC). One hypothesized impact of this transformation is the restoration of nutrients to the global pycnocline, without which biological productivity at low latitudes would be catastrophically reduced. Here we use a novel set of modeling experiments to explore the causes and consequences of the Southern Ocean nutrient return pathway. Specifically, we quantify the contribution to global productivity of nutrients that rise from the ocean interior in the Southern Ocean, the northern high latitudes, and by mixing across the low latitude pycnocline. In addition, we evaluate how the strength of the Southern Ocean winds and the parameterizations of subgridscale processes change the dominant nutrient return pathways in the ocean. Our results suggest that nutrients upwelled from the deep ocean in the Antarctic Circumpolar Current and subducted in Subantartic Mode Water support between 33 and 75% of global primary productivity between 30° S and 30° N. The high end of this range results from an ocean model in which the MOC is driven primarily by wind-induced Southern Ocean upwelling, a configuration favored due to its fidelity to tracer data, while the low end results from an MOC driven by high diapycnal diffusivity in the pycnocline. In all models, the high preformed nutrients subducted in the SAMW layer are converted rapidly (in less than 40 years) to remineralized nutrients, explaining previous modeling results that showed little influence of the drawdown of SAMW surface nutrients on atmospheric carbon concentrations.

Citation: Palter, J. B., Sarmiento, J. L., Gnanadesikan, A., Simeon, J., and Slater, D.: Fueling primary productivity: nutrient return pathways from the deep ocean and their dependence on the Meridional Overturning Circulation, Biogeosciences Discuss., 7, 4045-4088, doi:10.5194/bgd-7-4045-2010, 2010.
 
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